Various weeds developed on agricultural land and nonagricultural land, and many herbicides have been developed and tried for eradication thereof. Not limited to agricultural land and nonagricultural land, since the habitat of human and the land where weeds are developed tend to be located near in recent years, herbicides not only superior in the effectiveness but also having higher safety for human and the environment have been demanded.
For example, both ragweed and giant ragweed are annual grasses of Compositae Ambrosia, and wind-pollinated flowers causing pollinosis. In North America where they are originated, many patients with ragweed pollinosis are developed in summer and autumn every year and, in Japan also, ragweed pollinosis patients are present next to cedar or Japanese cypress pollinosis patients. The pathogenesis of ragweed pollinosis is highly probably ragweed and giant ragweed that grow in the neighborhood, and therefore, eradication of ragweed and giant ragweed developed nearby is effective as a measure for preventing ragweed pollinosis.
Also from the aspect of environment beautification, eradication of ragweed and giant ragweed provides a high merit. Ragweed and giant ragweed have very high vitality, attach and grow around the world as naturalized plants, and destroy the ecosystem of the invaded area. From the aspects of environmentology and conservation ecology, therefore, eradication of ragweed and giant ragweed has been desired.
Heretofore, various chemical substances having herbicidal activity are known. Many chemical substances having herbicidal activity also show high toxicity to other organisms, and many of them are not easily decomposed. In contrast, biological fatty acid, a salt thereof and an ester thereof are known as herbicides comparatively safe to the environment.
Patent document 1 discloses suppression of plant growth and partial or whole killing by a dispersion of 0.3-10% undecylenoic acid or a derivative thereof. Patent document 2 discloses a herbicidal active concentrated liquid containing fatty acid having a carbon number of 8-12, oil and a surfactant, which is suitable for emulsification in water. Patent document 3 discloses a herbicidal emulsion composition containing fatty acid having a carbon number of 8-12, a surfactant and water. Patent document 4 discloses a plant growth control (herbicidal) composition containing diol such as ethylene glycol and the like and fatty acid ester having a carbon number of 6-20.
However, undecylenoic acid used in patent document 1 is expensive due to the starting material and the lengthy production step, since it is produced by purifying a thermally-decomposed material of castor oil. When fatty acid itself is used, moreover, the odor causes problems. Furthermore, pelargric acid frequently used in patent documents 2-4 is expensive, since it is produced by an oxidation reaction of oleic acid. Since fatty acid itself is used in patent documents 2 and 3, the odor sometimes causes problems. In patent document 4, since fatty acid ester is used, the odor can be suppressed low. However, since ethylene glycol monofatty acid ester has one hydroxyl group and is hydrophobic as a whole molecule, an emulsion is obtained when diluted with water, and a transparent uniform aqueous solution (solubilized liquid) superior in the long-term stability is difficult to obtain even in the co-presence of a surfactant and the like.
[patent document 1] U.S. Pat. No. 2,626,862
[patent document 2] JP-A-5-501254
[patent document 3] JP-A-5-502216
[patent document 4] JP-A-7-509692